WO2009136030A1

WO2009136030A1 - Method of saving/restoring files in a peer-to-peer network

Info

Publication number: WO2009136030A1
Application number: PCT/FR2009/050560
Authority: WO
Inventors: Houssem Jarraya; Maryline Maknavicius-Laurent
Original assignee: Groupe Des Ecoles Des Telecommunications (Get) Institut National Des Telecommunications (Int)
Priority date: 2008-04-02
Filing date: 2009-04-01
Publication date: 2009-11-12
Also published as: FR2929792B1; FR2929792A1

Abstract

The present invention relates to a method of saving at least one file recorded by a peer in the memories of terminals of a plurality of nodes of a peer-to-peer network (1), in which: this peer is permitted to select a list of files to be saved; for each file, several data fragments (FB) and a description fragment (FBL) cataloguing the fragments FB are created; for each description fragment FBL, a key for locating the fragment and a key for encrypting this fragment FBL are generated; the fragments FB and the fragments FBL are saved in the terminals of a peer-to-peer network; at least one protected-access source fragment (9) making it possible to locate and to decrypt at least part of the fragments FBL is generated; and the source fragment (9) is saved in the memory of at least one terminal of the network.

Description

Method for backing up / restoring files in a peer-to-peer network

The subject of the present invention is a method for backing up / restoring files in a peer-to-peer network (hereinafter referred to as "P2P"). The term "P2P network" refers to a network composed of a set of entities called peers, interconnected with one another. Each of these entities can play both the role of server and client and it participates in the P2P service offered by the supply of some of its resources (hard disk, processor, ...) to the system.

The invention applies more particularly to information backup systems in P2P networks based on the use of a distributed hash table (DHT) and fragmentation of files.

The term "distributed hash table" denotes a data structure that associates for each peer a unique identifier that is the result of a hash function applied for example to its IP address or its machine name. Similarly, for each resource saved in the P2P network, there is associated a unique key of the same length as the peer identifiers. This key designated below by "DHT key" or "CDHT" is calculated by applying a hash function on an element of the resource, such as its name or content. Subsequently, each resource is saved in the peer whose identifier is closest to its key, according to a fixed distance function. C. Batten, K. Barr, A.Saraf and S.Trepetin are known from publications

"PStore: a secure peer-to-peer backup system" and Mr. Landers, H. Zhang and K.L. Tan "PeerStore: better performance by relaxing in peer-to-peer backup" examples of such backup systems.

In such systems, a peer fragments each file into several pieces of data called FB (File Block), and generates, for each of these files, an additional fragment called FBL (File Block List) that describes the list of FB fragments that make up the file. file and their location in the P2P network. The FBL fragment also contains additional information for recovering any version of the file. This FBL fragment is also saved in the P2P network and its location is identified by a DHT key.

With the pStore and PeerStore systems, simply store for each file its name and its path to be able to determine the DHT key and the decryption key. FBL fragment associated with the file. From a FBL fragment, the P2P system derives all the DHT keys and encryption keys associated with the FB fragments of the file; it then extracts the data fragments from a P2P network file and reconstructs the entire file. Also known by the website www.dispairse.point6.net another backup system in a P2P network.

In this example, each file saved in the P2P network consists of a set of fragments FB and a single fragment FBL 10, as shown in Figure 1. On the latter, it was assumed that two versions 20 and 21 d same file are saved. The fragment FBL defines for each version of the file and for each fragment FB a key for locating the fragment FB, in the example considered a DHT key (CDHT), and a key for decrypting the fragment FB (CC) and the length of the FB fragment.

With known backup systems, it is necessary to restore a file to know the DHT key to locate the FBL fragment, the key to decrypt this FBL fragment in order to recover any version of the file. These two keys are found from the file name, its path and a secret relative to the user (password or private key).

FIG. 2 shows a method of restoring a file saved in the P2P network with the known backup systems. The user must, from a terminal 3, specify the name and the path of the desired file in order to have access to the fragment FBL 10, this fragment FBL 10 allowing access to fragments FB 11 making it possible to reconstitute the searched file 13. With such backup systems, restoring N files assumes N identical and repeated FBL fragment extraction operations. The publication L.P. Cox, CD is still known. Muray and B.D. Noble

"Pastiche: making backup cheap and easy" another backup system defining its own file system and allowing the automatic backup and recovery of a file tree. This system associates for each file or directory a metadata file describing its contents. During the restoration phase, all you have to do is recover the metadata from the root folder so that you can later recover the entire file tree. Also known by the publication J. Cooley, C. Taylor and A. Peacock "ABS: the apportioned backup system" a system comprising a local database, duplicated itself in the P2P network, to keep the information necessary for restoration files. Thus, during the restoration phase, the user accesses his local database or retrieves it entirely from the P2P network to determine the list of data fragments needed to restore a file.

There is a need to further improve the methods for backing up and / or recovering automatically and securely personal files saved in a P2P network. The invention aims to meet this need.

According to one of its aspects, the subject of the invention is a method for saving at least one file recorded by a peer in the terminal memories of a plurality of nodes of a peer-to-peer network, in which:

- this peer is allowed to select one or more files to save,

- for each file, several data fragments (FB) and a description fragment (FBL) are created, listing the data fragments,

for each FBL fragment, a key for locating the FBL fragment in the network and a key for decrypting this fragment are generated; fragments (FB) and fragments (FBL) are saved in the terminal memories of a network; peer-to-peer

generating at least one protected access source fragment for locating and decrypting at least a portion of the FBL fragments and

the source fragment is stored in the memory of at least one terminal of the network.

By "memory", it is necessary to understand any type of data storage device, for example hard disk, magnetic tape, optical disk, electronic memories of the FLASH type, among others.

"Terminal" means for example a camera, a camera, a mobile phone, a smartphone, set-top box (for example of the "box" type connected to ADSL and providing telephone, internet and television), a computer, a laptop, a refrigerator, an oven, an alarm, a video recorder, an FTP server, a database server, an email server, a workstation or a digital personal assistant.

The invention makes it possible, thanks to the source fragment, to add a level in the hierarchy of the fragments FBL and FB of the prior art. The source fragment, by making it possible to locate and decrypt at least a portion of the description fragments of several files, enables the par to locate and decrypt fragments of these files saved in a single operation.

Unlike systems of the prior art, the peer no longer needs to memorize for each FBL fragment the key for locating the latter in the network and / or its decryption key.

The invention makes it possible, as soon as the source fragment is accessed, to be able to extract at one time files it automatically backs up in the P2P network, without having to request one by one the files it wishes to extract, which can be particularly useful in case of loss, either by crash or by theft, of the hard disk of the peer terminal.

The restoration of the backed up files depends only on the access to the source fragment, it can be done from any terminal of the network, and not only since the one from which the files to be restored have been saved.

When generating the source fragment, a key for encrypting the source fragment and a key for locating the source fragment can be computed.

The source fragment can be saved in the memory of one or more nodes of the network, or even in the memory of a secure element of the network, such as a backup server set up by an operator. The source fragment may directly contain the keys for locating and decrypting the FBL fragment (s), which may further simplify the decryption and localization of this fragment or fragments from the source fragment.

The key for locating the source fragment can be calculated by hashing at least one peer associated with the peer. This key is for example a DHT key. This key being dependent on a secret of the user, for example a password, a private key or a secret code associated with a terminal of the peer, for example a PIN code of a mobile phone , the invention may make it possible to prevent any node that does not know this secret from accessing the source fragment, thus making it possible to restrict access to the source fragment at the peer that has saved the files.

The key for encrypting the source fragment can be calculated according to at least one secret associated with the peer, for example according to a password, a private key or a secret code. The calculation function makes it possible, for example, to construct a symmetric encryption key from a string of characters by redistributing bits, deleting or adding other bits.

The use of such a key to encrypt the source fragment may make it possible to prevent another node, for example by a network backup server scanning technique, from reading and interpreting the source fragment to determine the list. backed up files and / or know who owns them.

The secret from which is calculated the key for encrypting the source fragment is for example the same as that from which is calculated the key to locate this source fragment.

The invention, by using keys to locate and encrypt the source fragment as mentioned above, makes it possible to condition the access to the source fragment and consequently the determination of the list of files that have been saved in the P2P network and / or their recovery to the knowledge by a node of the key for decrypting the source fragment and the key to locate it. The invention can thus make it possible to respect the privacy of the holders of the nodes of the network.

The method may comprise a step allowing the peer to select at least one property to be saved by file stored in the memory of a terminal of the network. These properties to be backed up are, for example, the access rights of local users, the creation date of the file or the path to this file.

The checksum of the file (checksum) to check the integrity of the file after it has been restored can also be saved, which can detect errors during the file restore, these errors can be caused by a collision between FB fragments. The method may comprise the step of allowing the peer to modify a source fragment already generated to take into account: the backup of a new file saved in the memory of a network terminal and / or the deletion of a saved file

According to an exemplary implementation of the invention, the source fragment makes it possible to locate and to decipher all the generated FBL fragments, which can allow a peer to have only one source fragment from which it can, if he wishes, restore all the files he has saved.

According to another exemplary implementation of the invention, several source fragments can be generated, each source fragment making it possible to locate and to decipher part of the FBL fragments associated with the files saved, which can make it possible to associate a source fragment with group of files saved.

A key for locating or encrypting a source fragment can be calculated in the same way as previously defined.

The keys for locating and encrypting the source fragments may be different from one source fragment to another, which may prevent a node that knows the keys of a source fragment from gaining access to the other fragments. sources, but also collisions between source fragments.

Files can be grouped into a particular source fragment depending on their type, content, or access rights.

File types according to the invention are, for example, photos, videos, sound recordings or texts.

Still according to this exemplary implementation of the invention, a root fragment for locating and decrypting the source fragments can be generated, this root fragment can be saved in the memory of at least one P2P network terminal. Another object of the invention is, according to another of its aspects, a method of restoring at least one file saved in the terminal memories of a peer-to-peer network in the form of data fragments (FB) to which is associated a fragment of description (FBL) listing the fragments of data, this fragment FBL being localizable and decryptable by a protected access source fragment saved in the memory of a terminal of the network, in which process: a peer accesses the source fragment from any terminal in the network to determine the list of files backed up in the network, the peer selects at least one file to be restored from the list, the peer initiates the process of automatically restoring the selected file (s) from this terminal.

The method may comprise a step of updating the list of the files saved, for example to take into account the peer backup of a new file in the network or the deletion of a file in the network.

The method may include a step of testing availability and integrity on files in the list. These tests can be performed periodically to ensure that the restoration process is operational and may concern only one file, or even more or even all of the files in the list.

Another aspect of the invention is a method of selective broadcasting of at least one file recorded in the terminal memories of a peer-to-peer network, this file being fragmented into several pieces of data ( FB) associated with a description fragment (FBL) listing the FB fragments, this FBL fragment being localizable and decryptable by a protected access source fragment saved in the memory of a terminal of the network, a method in which a client is allowed of the network searching for the recorded file and having satisfied a predefined condition the access to the source fragment and the recovery of the searched file.

Access to the searched file may be enabled by providing the network client with a key for locating the source fragment and / or a key for decrypting the source fragment. The key to locate and / or the key to decrypt the source fragment is for example specific to each client, which can allow by assigning personal keys to each client to limit the risk of fraudulent access to the file.

The method may include a step of testing availability and integrity on the file. This test can be performed periodically to ensure that the broadcast process is operational.

Another subject of the invention is, according to another of its aspects, a method for saving at least one file recorded by a peer in the terminal memories of a plurality of nodes of a peer-to-peer network, each file being fragmented into a plurality of data fragments (FB) to which is associated a description fragment (FBL) listing the data fragments, in which process: least one source fragment for locating and decrypting at least a portion of the FBL fragments,

generating for this source fragment a key for locating and a key for encrypting the source fragment according to a secret of the user, and

The P2P network can be a home automation private network.

In a variant, the P2P network is an enterprise private network, distributed or not on several geographically distant sites.

In another variant, the P2P network uses the Internet network. The invention will be better understood on reading the following description, of non-limiting examples thereof, and on examining the appended drawing, in which:

FIGS. 1 and 2 illustrate an example of a method for backing up and restoring already known files,

FIGS. 3 and 4 illustrate files backup and restoration systems according to the invention,

FIG. 5 schematically represents an example of source fragment according to the invention,

FIGS. 6 and 7 illustrate an example of a file saving method and an example of file restoration according to the invention, and FIGS. 8 to 16 show examples of application of the invention.

FIGS. 3 and 4 show an example of backup by a pair of 13 _X files according to the invention. For example, each _X file is fragmented into several data fragments (FB) 11 to which is associated a description fragment (FBL) listing the FB fragments, similar to the known systems described above. As can be seen in FIG. 4, the fragments FBL 1O ₁ and FB 1 I _j can be recorded in the memories of terminals 3 constituting a peer-to-peer network 1, these terminals possibly being different from that of the peer having recorded the files. 13 ^ Although the terminals 3 are represented in the form of computers in FIG. 4, the invention is of course not limited to the use of such terminals, as will be seen later.

According to the invention, at least one source fragment 9 is stored in the memory of a terminal 3 of the network 1, this terminal being in the example described different from the terminal of the peer having recorded the files 13 ^

For security reasons, the source fragment 9 may be stored in the memory of several distinct nodes and / or be recorded in a not shown backup server. Such a backup server can be set up by an operator or other trusted entity.

As can be seen in FIG. 3, the invention makes it possible to add a level of hierarchy to the fragments FBL 1O ₁ and FB H _j thanks to the source fragment 9 which allows the localization and the decryption of all the fragments FBL 1O ₁ and, via the latter, the location of all fragments FB 1 I _j constituting a file 13 ^ the invention allows, in this example, the user no longer necessarily have to memorize an element of information allowing him to find the DHT key and / or the encryption key of one of its fragments FBL.

FIG. 5 shows an example of source fragment 9. This fragment contains different fields. A first field 30 assigns an identifier / number to the file 13i. A second field 31 lists the name of the recorded _X file. A third field 32 corresponds to a key, for example a DHT key, making it possible to locate the fragment FBL 1O ₁ associated with the file 13 _X

A fourth field 33 corresponds to a key making it possible to decrypt the fragment FBL 1O ₁ associated with the file 13 ^ Access to the source fragment 9 is protected by two keys, a key to allow the location of the source fragment 9 in the network 1, by example a DHT key, and a key to allow its encryption in the case of file backup or decryption in the case of file restoration or file distribution.

These keys are determined in the example described from a secret only known to the user and which can take the form of a password, a private key, a secret code such as a code PIN of a terminal, for example a mobile phone or a personal digital assistant belonging to the peer. The DHT key is for example determined by hashing the password or the private key or the PIN code.

The key for encrypting or decrypting the source fragment 9 is for example calculated according to the password, the private key or a secret code. This calculation function makes it possible, for example, to construct a symmetric encryption or decryption key from a string of characters by redistributing these bits, deleting or adding other bits.

The various fragments saved in the network 1 relating to the backup of a file 13 _X are therefore encrypted: the data fragments FB 11 using, for example, the method "Convergent Encryption" as disclosed in the publication JR Sweetness, A. Adya, WJ. Bolosky, D. Simon and M. Theimer "Reclaiming space from duplicate files in a serverless distributed file system", the fragments FBL 1O ₁ using the symmetric encryption key saved in the source fragment 9, and the source fragment 9 using a key calculated from of the peer's secret. In case a node wants to access, without permission, a saved file

13 _l5 it must first determine the keys allowing access to the source fragment 9. These keys being, as mentioned above, determined from a secret of the user, no unauthorized node can access the source fragment 9 and therefore the saved files 13 _X Thus, no unauthorized node can not access a file without the authorization of its owner, nor determine the list of files saved in the network 1.

Saving all the data associated with the peer, both the useful data and the metadata, in the network 1, ensures that the process of restoring these files can start, even without a hard disk or in case of hard disk crash entirely, from any terminal 3 connected to the network 1.

The source fragment 9 may further comprise, as shown in FIG. 5, other fields 34 containing properties of the saved file 13 _X. These properties concern for example the access rights of local users, the creation date of the file or the file path.

Field 34 may also contain a checksum to check the integrity of the entire file after it is restored. This check detects errors due to a collision between FB fragments, these errors being considered negligible.

The method used in backup systems such as pStore or

PeerStore consists of separately checking the integrity of each FB fragment. This parcel checking of the integrity of a file can be problematic when a collision between fragments occurs, that is, if another different FB fragment but having the same DHT key value is stored instead a fragment of this file. Collision detection is not possible in the case of parcel control, but the collision problem can be detected if the global integrity check on the entire file is performed through the source fragment 9.

The invention enables the peer to access the source fragment 9 provided that it has communicated its secret, namely its password, its private key, its secret code or its PIN code, on the basis of which the keys allowing locate and decrypt the source fragment 9 will be determined, then recover all the files that have been saved in the P2P network.

FIG. 6 represents an exemplary method of saving files in a network 1 as represented in FIGS. 3 and 4.

At a first step 100, the peer selects the list of files it wishes to save in the network 1. At step 110, the peer selects one or more properties to be saved, these properties corresponding to those mentioned in relation to the field 34 of the source fragment 9.

In step 120, the peer specifies the importance level of the saved information. In step 130, the fragments FB H _j are created by applying the necessary security processing and saved in the network 1, and a fragment FBL 1O ₁ is associated for each 13 _X file saved.

In step 140, the peer generates for each fragment FBL 1O ₁ a location key and an encryption key, decrypts the fragment and the backup in the network 1.

In step 150, a source fragment 9 is generated with calculation of keys for locating and encrypting this source fragment 9. In step 160, the peer saves this source fragment 9 in the network 1 in the memory of one or more computer terminals 3 of the network and / or in the memory of a backup server.

FIG. 7 shows an example of a method for restoring by a peer one or more files saved according to the invention, this restoration method being able to be performed from any terminal 3 of the network and not only from the terminal with which the For example, par has performed the process shown in FIG.

In step 200, the user presents the secret he used to associate an encryption key and a location key with his source fragment 9. In step 210, the peer retrieves and decrypts the source fragment 9.

In step 220, the peer determines the list of 13 _X files it has saved in the network 1. The viewing of these files can be in the form of a flat list of file names, or a tree highlighting the path originally occupied by each saved file. In step 230, the peer selects the number of files it wishes to restore, namely one, several or all of the files 13 ^

In step 240, the automatic restoration of this or these files begins with the recovery of its fragment FBL 1O ₁ and its data fragments FB 1 I _j .

A peer can also recover its source fragment 9 to take into account the saving of a new file in the network 1 and / or the deletion of a file from the network 1 and / or to perform availability and integrity tests on one or more files saved 13 ₁₅ so as to ensure, periodically or in a controlled manner by the user, that the backup method is operational.

Several examples of applications of the invention will now be described with reference to FIGS. 8 to 16.

FIG. 8 shows an example of application of the invention to a home automation private network 1.

This network 1 comprises for example a plurality of appliances

"Intelligent" and / or electronic devices such as a camera, a camera, a mobile phone, a set-top box, a computer, a refrigerator, an oven, an alarm, a video recorder, these devices each having a memory and corresponding to computer terminals 3i within the meaning of the invention. All or part of these devices can communicate by carrier or non-wireless link, for example Bluetooth or Wifi type.

By creating a peer-to-peer network 1 whose nodes are made up of these different devices, a user can create his own distributed file recovery system. Indeed, it can keep a copy of the important files of a node, for example the computer 3i or 3 ₂ , on the other nodes of the network P2P in order to recover them in case of loss of the original files due to the loss of the disk hard terminal 3i or 3 ₂ .

According to this example, the invention makes it possible to benefit from a new free and normally reliable restoration system, the nodes being under the entire control of the user.

In the example described, the different nodes of the network 1 can share the same source fragment, which makes it possible to recover, thanks to the source fragment, any file from any node, independently of the node from which the file has been registered. FIG. 9 shows another example of application of the invention to produce a system for restoring files in a corporate private network 1, including servers, for example FTP servers, database servers. or email servers, and workstations that correspond to terminals within the meaning of the invention, constitute a peer-to-peer network. In this example, the free disk spaces of the memories of the various terminals 3 are used to record files, making it possible to duplicate the important data of a node on the other nodes of the network 1 in order to restore them in case of loss of the initial files.

The invention allows the company to benefit from a file restoration system: free, the company does not need to reserve a particular server to duplicate the important data of its various terminals 3, reliable, all the nodes being under the entire control of the company and, of course, the terminals 3 being in this example servers and workstations of the company, these different machines being always available in the network, so that the backup and the Restoring a file in Network 1 can be done at any time. The example of FIG. 10 differs from that of FIG. 9 in that the enterprise is distributed on several geographically distant sites in which local intranets I ₁ , I ₂ and I ₃ similar to the network described with reference to FIG. 9 exist. In the example of FIG. 10, communication between local intranet networks of two remote geographical sites is secured by establishing a VPN tunnel 2 created by one of the following protocols: Layer Two Tunneling Protocol (L2TP), IPsec (Internet Protocol) Security) or MPLS VPN.

The invention, by making it possible to save node files of a geographical site in memory of nodes of other geographical sites, allows the restoration of these files even in the case where the geographical site in which the terminal of the node is located having saved the files would disappear in its entirety due for example to a fire, a natural disaster or an attack.

In the example of FIG. 10, the company assigns, according to a first embodiment, to each geographic site a single source fragment 9 enabling the automatic restoration of all the important data of a site. The secret allowing access to this source fragment is preferably known only by the site manager.

According to a second embodiment, the company allocates for each service of each geographical site, for example the financial or commercial service of each geographical site, a single source fragment. In this example, the source fragment allows the automatic restoration of all the important data of a service and its secret is advantageously known only by the director of the service.

According to a third embodiment, the company assigns each terminal 3 a source fragment 9. In this example, the source fragment 9 only allows the automatic restoration of important data of a particular terminal and its secret is advantageously known. than the owner of this terminal.

FIG. 11 shows another example of application of the invention.

In this example, the peer-to-peer network 1 is formed by nodes that are terminals 3 connected to the Internet.

The terminals 3 are in this example chosen from computers, mobile phones, set-top boxes (for example of the "box" type connected to ADSL and providing telephone, internet and television) and PDAs. In this example, a peer keeps a copy of its important data in the disk spaces of the memory terminals of the other nodes of the network 1, in order to recover them in case of loss of its local data.

If applicable, a mobile or fixed operator, an access provider, or a new P2P service provider may charge the proposed backup and restore service to the peer.

In this example application, if the user is the owner of a single node, a single source fragment allowing him to automatically restore from any node, all of his data already saved in network 1 can be assigned.

Also in this example application, if the user is the owner of several nodes, he can choose between:

- share a single source fragment between its different nodes. Thus, it is possible for him to automatically restore all his files already saved in the network 1 independently of the node from which the file backup took place;

- assign each of its nodes a different source fragment. In this case, the automatic restore process will be restricted to single node files,

- assign each of its nodes a different source fragment and create a root fragment to locate and decrypt the source fragments specific to each of its nodes. In this case, the automatic recovery process can include all files already backed up in network 1 or be restricted to files of only one node;

To ensure the proper functioning of the backup and / or restore method, the network 1 may comprise, as represented in FIG. 12, a central trusted entity 5 in periodic communication with all the nodes 3 of the network 1 and arranged to:

- avoid selfish behavior of nodes by counting, for example, the resources provided and consumed by each node. A credit or debit billing system can be provided depending on whether the resources provided are more or less important than the resources consumed;

- control access to the proposed P2P service; - control the behavior of the various nodes during the operation of the system, by periodically checking that each node performs the assigned work, that it is available, that previously saved fragments are always well saved and intact. This makes it possible, for example, to evaluate the level of reliability of a node on which the billing associated with a node could be based;

- ensure a good quality of service to users.

To allow the authorization of a peer to perform a backup and / or restore method according to the invention, several solutions are possible:

- use of a specific home automation box so that all network equipment in the house can benefit from it;

- software in the specific mobile allowing to save only the data of this mobile;

- passing through a proxy service provider, allowing the peer to access and restore its data regardless of the host machine (mobile, PC ...); - obligation to have an access token signed by a trusted node which is responsible for controlling access to the proposed service;

- obligation to have access to a particular node of the network, access being restricted to only those entities authorized to make P2P service.

Access to the source file may be controlled by a mobile or fixed operator, an access provider or a P2P service provider. The access control may consist, for example, of an AAA control device (Authentication, Authorization,

Accounting). This particular node can then be responsible for controlling the good behavior of the nodes during the various backup operations but also in the duration.

The invention is not limited to backing up and / or restoring files backed up in a peer-to-peer network.

According to other applications, it allows the selective broadcast in a peer-to-peer network of at least one file, for example a multimedia or musical content, for example one or more films or music files, game software, professional or other, stored in the memory of at least one terminal of the network. By broadcasting the secret allowing calculation of the DHT keys and decryption associated with the source fragment 9 to a group of users, it is possible, thanks to the invention, to distribute data to this group of users, which may allow to obtain the equivalent of a "virtual" server, insofar as the files to be distributed are saved in the memories of different terminals s.

FIG. 13 shows such an example of application of the invention. A node 6 of the network 1, hereinafter called server node acts as a server distributing films, multimedia content for example, other nodes 8 of the network 1, hereinafter called clients. Unlike a centralized video on demand server, it is not thanks to the invention not necessary to use a DNS name or a large storage space.

According to the example shown in FIG. 13, the server node 6 firstly stores in the memories of the terminals 3 of the network all the films 13 _X to be shared with the clients of the network 1.

The server node 6 then calculates from a secret the location key and the encryption key allowing access to the source fragment 9 listing all the 13i films saved then creates and saves its source fragment in the memory of n ' Any terminal of the network 1. The server node 6 then transmits the secret allowing access to the source fragment to any client 8 of the network 1 having satisfied a predefined condition being for example the subscription to a subscription.

The dissemination of the secret allowing access to the source fragment can take several forms. By the knowledge of the secret, a client 8 can retrieve and decrypt the source fragment 9 of the server node 6 and thus determine the list of films that are available. Moreover, from the information contained in this source fragment, it can recover any movie H ₁ already saved by the server node in the network 1.

Although the data of the server node 6 is saved in the terminal memories 3 of different nodes of the network, only the nodes having access to the source fragment 9 can access the movies 13.

To share a new movie, the server-node 6 can save it in the network 1 and then update its source fragment 9. By recovering the new version of this source fragment, a client 8 can determine the new list of films offered by the server node 6. The server node 6 can, at any time, remove films from the network 1, for example in order to free disk space in the memories of the terminals 3 to save new movies.

According to this example, the invention makes it possible to have an accessible service even if the server node 6 is inaccessible since all the necessary information is saved and distributed on the various nodes of the P2P network.

The secret allowing access to the source fragment 9 can be distributed to the clients 8 in several forms:

- a password or PIN code: the same character string is communicated to the customers. This string is to be entered in the access software to the data distribution application.

a secret, such as a private key, communicated to the customers on a protected physical medium, for example an electronic chip or a USB key.

a custom client-dependent secret, being determined according to certain characteristics of this client, for example the MAC address of the terminal that it uses. The user downloads a client software to which he must enter the personalized secret. The software can then calculate the secret allowing access to the source fragment according to this personalized secret. The custom secret can still be determined using other characteristics of the customer, such as his subscriber number when he has subscribed to an operator.

The communication of the secret allowing access to the source fragment or, where appropriate, the personalized secret can take the following forms:

- communication of the secret by email or postal mail,

- download by the client software the secret from an online server. Downloading from the server can be considered almost transparent for the user. In addition, the client software can provide a serial number or a client name so that the server controls the dissemination and personalization of the secret,

- download by the user of the secret from an online server. After having authenticated with this server, the user downloads the secret, for example, and configures his client software accordingly. As a variant, the file to be broadcast is a file relating to an advertisement or of an informative nature and the server node 6 can broadcast the secret to all the clients 8 of the network 1 having made the request.

The modification rights of the source fragment, to add or delete a new file saved, can be reserved to the server node 6 to prevent a client to whom the secret was revealed can not modify the saved contents. This control of these rights of modification of the source fragment can be ensured by a centralized server in which are memorized all the source fragments of the network, and which grants the rights of modification only to the node-server 6 and gives the right only to clients 8.

In another example of an application, the invention enables the sharing of files between the nodes of the network 1 by the knowledge of a source fragment 9. The principle is identical to the principle of broadcasting a file by a server node 6 to a client 8 described above, except that the modification rights of the source fragment are open to all the nodes of the network. The same services are possible, namely the secret access control of the source fragment 9, the updates of the source fragment 9, and the management of the different versions of the saved files 13 _L

The invention can also allow the creation of a root fragment for locating and decrypting a plurality of source fragments 9 saved in the network 1. In the example shown in FIG. 14, the root fragment 7 makes it possible to locate and decrypting first source fragments 9a, the latter making it possible to locate and to decipher second source fragments 9b which are similar to the source fragments described with reference to the preceding figures. In this example, access to each source fragment 9a or 9b is conditioned by the knowledge of a secret according to the examples described above. The secret is different from a first source fragment 9a to another, as well as from a second source fragment 9b to the other. Thus, access to a single source fragment only allows the recovery of a subset of files. Only the access to the root fragment 7, conditioned for example by the knowledge of a secret making it possible to calculate keys to locate and decipher the root fragment, can allow the access to all the source fragments and the complete recovery of the files saved in the network 1.

In this example, the first source fragment 9ai contains keys for locating and decrypting the second source fragments 9bi, 9b ₂ and 9b3, which allows to locate and decrypt the fragments FBL 1Oi to IO5 and IO7, and therefore access to the files 13i to 13s and 13 ₇ .

According to this example, the invention can allow the peer having saved the files whose restoration is allowed through the access to the root fragment 7 to broadcast only a subset of files to a client of the network. If this client can, according to the example of FIG. 14, access only the second source fragment 9bi, it can only recover the fragments FBL 1O1 to IO3 and consequently only recover the files 13i to 133-

In this example, the peer may decide to share only a subset of files that it has backed up with other nodes in the network. The peer can choose to share only the 13s and 13 ₇ files with one or more nodes of the network by sending them the secret allowing them to access only the second source fragment% ₃ .

Still according to this example, the invention also makes it possible to optimize the disk space volume of the memory of the terminals 3i by allowing several first source fragments 9a to point to one and the same second source fragment 9b, or even to several same second source fragments. 9b. In the same way, several second source fragments 9b can point to the same FBL fragment 10, or even to several same FBL fragments.

FIG. 15 shows an example of application of the invention in which two root fragments 1 1 and 7 ₂ associated with two different pairs point to the same source fragment 9 ₀ . This source fragment 9o makes it possible, for example, to access all the files shared between the two peers.

Thus, each of the peer having access to the root fragment 1 \ and the one having access to the root fragment 7 ₂ can be considered as the owner of the source fragment% and the files to which access is thus allowed, although these files are not saved. only once in the network.

The peer having saved the files whose access is allowed by the root file does not need to retain the secrets allowing access to the different source fragments or, when the source fragments are hierarchized into first and second source fragments, the secrets allowing access to these different source fragments, but only that of the root fragment, the latter advantageously containing the secrets allowing access to the source fragments. In the case of the example of FIG. 14, if a server node 6 wishes to allow a client to access all the files it has saved in the network, it is sufficient to communicate to it the secret permitting access to the root fragment 7, in this way it will be able to obtain the list of the first source fragments 9a, allowing themselves access to the second source fragments 9b.

FIG. 16 shows an example of a method for distributing files saved within different source fragments 9.

In the example shown, for each type of backup file, a source fragment 9 is associated. The source fragment 9 is for example only related to files containing photos, which enables the peer to restrict its automatic restoration to all of his photos that have been saved in the network 1.

In another example, the files saved are grouped according to their contents. For example, a server node offering video films can associate each category of films (cultural, sport, ...) with a source fragment 9. Subsequently, a customer can subscribe to a particular category of films by asking the secret allowing access to the source fragment 9.

In another example, the files saved are grouped according to the access rights by the nodes of the network to the files saved. For example, private files are associated with a source fragment whose secret may never be transmitted to the other nodes of the network, and we associate with the public files another source fragment whose secret can be transmitted to all the nodes of the network.

Because of the property of optimization of the volume of memory disk space previously described, the invention can make it possible to group the files saved in a database of multi-criteria source fragments, the number of source fragments and hierarchy of source fragments, ie first, second ... nth ^source fragments increasing with the number of criteria.

The invention is of course not limited to the examples which have just been described.

For example, characteristics described with reference to various embodiments of the invention may be combined.

Claims

A method of saving at least one file (IS ₁ ) registered by a peer in the terminal memories (S ₁ ) of a plurality of nodes of a peer-to-peer network (1), wherein:

- this peer is allowed to select a list of files to save,

for each file (IS ₁ ), several data fragments (FB) (1 I _j ) and a description fragment (FBL) (1O ₁ ) listing the FB fragments are created,

for each fragment FBL (1O ₁ ) of description, a fragment location key and an encryption key of this fragment FBL (1O ₁ ) are generated,

the fragments FB (1 I _j ) and the fragments FBL (10 ₁ ) are saved in the terminals (S ₁ ) of a peer-to-peer network

generating at least one protected access source fragment (9) making it possible to locate and decrypt at least a portion of the FBL (1O ₁ ) fragments, and the source fragment (9) is saved in the memory of at least one terminal (S ₁ ) of the network.

2. Method according to claim 1, wherein during the generation of the source fragment, a key is computed for locating the source fragment and a key for encrypting the source fragment.

3. Method according to the preceding claim, wherein calculating the key for locating the source fragment (9) by hashing at least one secret associated with the peer.

4. The method of claim 2 or 3, wherein calculating the key for encrypting the source fragment (9) according to at least one secret associated with the peer.

5. Method according to one of the two immediately preceding claims, wherein a secret associated with the peer is selected from a password, a private key, and a secret code associated with a terminal of the peer.

6. Method according to any one of the preceding claims, wherein the peer is allowed to select at least one property to be saved by file recorded in the network terminal memories.

7. Method according to the preceding claim, wherein said at least one property is selected from the checksum of the file (checksum) and / or the date of creation of the file and / or the access rights to the file and / or the file path and / or file version.

A method as claimed in any one of the preceding claims, wherein the peer is allowed to specify the level of importance of the saved file.

9. Method according to any one of the preceding claims, in which the peer is allowed to modify a source fragment (9) already generated to take into account: the saving of a new file (IS ₁ ) in the terminal memories ( S ₁ ) of the network and / or the deletion of a saved file.

10. Method according to any one of the preceding claims wherein the source fragment (9) makes it possible to locate and to decipher all the generated FBL (1O ₁ ) fragments.

11. Method according to any one of claims 1 to 9, wherein generating several source fragments (9), each source fragment (9) for locating and decrypting part of the generated FBL (1O ₁ ) fragments.

12. Method according to the preceding claim, wherein for each source fragment (9), two keys are calculated, one for locating and the other for encrypting the source fragment (9).

13. The method according to the preceding claim, wherein the keys for locating and encrypting the source fragment (9) differ from one source fragment to another.

14. Method according to one of the two immediately preceding claims, in which the files (13) stored in a particular source fragment (9) are grouped together according to their type, their content or the access rights associated therewith.

15. Method according to any one of claims 11 to 14, wherein a root fragment (7) is generated for locating and decrypting the source fragments (9) and in which this root fragment (7) is saved in the memory. at least one terminal (3i) of the network.

16. A method for selectively distributing at least one file (13 ^ stored in the memory of at least one terminal (3i) of a peer-to-peer network (1), this file (13 ^ being fragmented into several fragments of FBI data (H _j ), with which is associated a description fragment (FBL) (1O ₁ ) listing the fragments (FBL) (H _j ), these fragments FBL (1O ₁ ) being localizable and decryptable by a protected access source fragment (9) stored in the memory of a terminal of the network, a method in which a client (8) of the network looking for the recorded file (IS ₁ ) and having satisfied a predefined condition the access to the source fragment (9) and the recovery of the searched file.

17. The method as claimed in the preceding claim, in which access is granted to the searched file (IS ₁ ) by providing the client (8) of the network with a key making it possible to locate the source fragment (9) and / or a key making it possible to decrypt the source fragment

(9).

18. The method according to the preceding claim, wherein the key for locating and / or the key for decrypting the source fragment is customer-specific (8).

19. Method according to any one of claims 16 to 18, comprising a step of testing the availability and integrity of the file sought.

20. Method for restoring at least one saved file (IS ₁ ) in the terminal memories (S ₁ ) of a peer-to-peer network in the form of data fragments

(ll _j ) with which is associated a description fragment (1O ₁ ) listing the data fragments, this description fragment being localizable and decipherable by a protected access source fragment (9) saved in the memory of a terminal of the network, method in which: - a peer accesses the source fragment (9) for, from any terminal of the network, determine the list of files saved in the network

the peer selects at least one file to be restored (IS ₁ ) in the list,

- the peer initiates the process of automatic restoration of the selected file (s) from this terminal.

21. Method according to the preceding claim, comprising a step of updating the list of saved files.

22. Method according to one of the two immediately preceding claims, comprising a step of testing availability and integrity on files listed in the source fragment.

23. A method of saving at least one file (13i) recorded by a peer in the terminal memories (3 ^ of a plurality of nodes of a peer-to-peer network, each file being fragmented into several data fragments ( H _j ) which is associating a description fragment (1O ₁ ) listing the data fragments, wherein:

generating at least one source fragment making it possible to locate and decrypt at least a part of the description fragments, generating for this source fragment a key for locating and a key for encrypting the source fragment (9) according to a user secret, and